Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already communicate readOnly, idempotent, and non-destructive nature. The description adds important behavioral context: 'static local response — no API call, never rate-limited' and instructs agents to hand the URL to the user and 'must NOT attempt to complete the subscription themselves'. These details go beyond what annotations provide.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is concise, using three short paragraphs each with a distinct purpose: purpose/use case, behavior, and return values/agent action. Every sentence adds value, and the most important information is front-loaded.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple static tool, the description fully covers when to use it, its behavioral characteristics, the return fields, and an explicit agent instruction. The presence of an output schema handles return-value details, so no gaps remain.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema covers the single optional 'tier' parameter with an enum and description ('only "pro" supported today'), achieving 100% schema coverage. The description adds no additional parameter semantics, so the baseline score of 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'Get the URL where the user can subscribe to FreightUtils Pro for higher API limits', using a specific verb and resource. It is distinct from all sibling tools, which are calculators or lookups and have no subscription-related purpose.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly gives when-to-use: 'when the user asks how to upgrade or about pricing, or after any other tool errors with a 429 rate_limited body.' It does not mention when-not-to-use, but given there are no sibling subscription tools, no alternative is available. The guidance is clear and actionable.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.